U.S. patent application number 13/847966 was filed with the patent office on 2013-10-31 for method for preparing an anion exchange membrane with ion exchange groups and an apparatus for removal of ions.
This patent application is currently assigned to VOLTEA B.V.. The applicant listed for this patent is Piotr Edward Dlugolecki, Henricus Marie Janssen, Hank Robert Reinhoudt, Albert Van Der Wal, Michel Henri Chretien Joseph Van Houtem. Invention is credited to Piotr Edward Dlugolecki, Henricus Marie Janssen, Hank Robert Reinhoudt, Albert Van Der Wal, Michel Henri Chretien Joseph Van Houtem.
Application Number | 20130284601 13/847966 |
Document ID | / |
Family ID | 47882107 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130284601 |
Kind Code |
A1 |
Van Der Wal; Albert ; et
al. |
October 31, 2013 |
METHOD FOR PREPARING AN ANION EXCHANGE MEMBRANE WITH ION EXCHANGE
GROUPS AND AN APPARATUS FOR REMOVAL OF IONS
Abstract
A method of preparing an anion exchange membrane with anion
exchange groups. The method includes polymerizing a first monomer
with a functional group selected from the pyridine derivatives with
a second monomer selected from the benzene derivatives, such as
styrene, to form a copolymer. The copolymer may be crosslinked with
a crosslinker. The functional group of the copolymer may be
functionalized to an anion exchange group.
Inventors: |
Van Der Wal; Albert;
(Oegstgeest, NL) ; Dlugolecki; Piotr Edward;
(Gdansk, PL) ; Reinhoudt; Hank Robert; (Wassenaar,
NL) ; Van Houtem; Michel Henri Chretien Joseph;
(Eindhoven, NL) ; Janssen; Henricus Marie;
(Eindhoven, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Van Der Wal; Albert
Dlugolecki; Piotr Edward
Reinhoudt; Hank Robert
Van Houtem; Michel Henri Chretien Joseph
Janssen; Henricus Marie |
Oegstgeest
Gdansk
Wassenaar
Eindhoven
Eindhoven |
|
NL
PL
NL
NL
NL |
|
|
Assignee: |
VOLTEA B.V.
Sassenheim
NL
|
Family ID: |
47882107 |
Appl. No.: |
13/847966 |
Filed: |
March 20, 2013 |
Current U.S.
Class: |
204/630 ;
521/27 |
Current CPC
Class: |
C02F 1/4691 20130101;
C08F 226/06 20130101; B01D 71/62 20130101; B01D 2323/30 20130101;
C08J 5/2243 20130101; B01D 2325/42 20130101; B01D 67/0006 20130101;
B01D 71/28 20130101; B01D 71/76 20130101; B01J 41/14 20130101 |
Class at
Publication: |
204/630 ;
521/27 |
International
Class: |
B01J 41/14 20060101
B01J041/14; C02F 1/469 20060101 C02F001/469 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2012 |
NL |
2008516 |
Claims
1. A method of preparing an anion exchange membrane with anion
exchange groups, the method comprising: reacting at least a first
monomer comprising vinyl-pyridine with a pyridine derivative as a
functional group with at least a second monomer comprising styrene
to form a substantial linear copolymer; and reacting the
substantially linear copolymer with a crosslinker, the crosslinker
reacting with the pyridine derivative group of the substantially
linear copolymer crosslinking the substantially linear copolymer
and forming the anion exchange groups.
2. The method according to claim 1, wherein the molar ratio of the
first monomer to the second monomer is 1:1 to 4.
3. The method according to claim 1, wherein each of the first and
second monomers comprise a vinyl group and the reacting step to
form a copolymer comprises using an initiator and a chain transfer
agent to react the vinyl groups with each other.
4. The method according to claim 3, wherein the chain transfer
agent comprises a thiol group.
5. The method according to claim 3, wherein the first and second
monomers and the chain transfer agent are provided in a molar ratio
of from 1:1 to 4:0.005 to 0.03 to form the copolymer.
6. The method according to claim 1, wherein the crosslinker is a
compound of the group of dihalocarbons.
7. The method according to claim 6, wherein the dihalocarbon is a
dihalo-alkane selected from: 1,6-diiodohexane,
1,5-diodobromopentane, 1,6-dibromohexane and/or
1,10-dibromodecane.
8. The method according to claim 1, wherein the anion exchange
groups are formed by reacting the copolymer and/or the crosslinked
polymer with a monohalocarbon before and/or during the reacting
step of the copolymer with the crosslinker.
9. The method according to claim 1, wherein the anion exchange
groups are formed by a quaternization reaction between the pyridine
derivative and a monohalide and/or dihalide.
10. The method according to claim 1, wherein the reaction of the
copolymer with the crosslinker is carried out at least partially on
a surface of a first electrode.
11. The method according to claim 1, wherein the first monomer
comprises at least one monomer selected from the following:
4-vinylpyridine; 3-vinylpyridine; 2-vinylpyridine;
2-methyl-5-vinylpyridine; and/or 5-ethyl-2-vinylpyridine.
12. The method according to claim 1, wherein the second monomer
comprises an apolar or polar styrene derivate.
13. The method according to claim 1, wherein the second monomer
comprises at least one monomer selected from the following:
4-tert-butoxystyrene; 2,4-dimethylstyrene; 2,5-dimethylstyrene;
3-methylstyrene; 4-methylstyrene; 2,4,6-trimethylstyrene
3,4-dimethoxystyrene; 4-methoxystyrene; 3-hydroxystyrene;
4-hydroxystyrene and/or 4-acetoxystyrene.
14. The method according to claim 1, wherein the number of pyridine
groups as derived from H NMR data is between 1 to 5 Mol/Kg
copolymer and/or the number average molecular weight (Mn) of the
copolymer is between 2 and 5 Kg/mol and the weight average
molecular weight (Mw) of the copolymer is between 7 and 15
Kg/mol.
15. An apparatus for removal of ions, the apparatus being provided
with: a first and second electrode; and an anion exchange membrane
on the first electrode, wherein the anion exchange membrane is
obtained by crosslinking a substantially linear copolymer according
to the method of claim 1.
Description
[0001] This application claims priority from Netherlands Patent
Application No. NL2008516, filed Mar. 21, 2012, which is
incorporated herein in its entirety by reference.
FIELD
[0002] The present invention relates to preparing an anion exchange
membrane with anion exchange groups.
BACKGROUND
[0003] In recent years one has become increasingly aware of the
impact of human activities on the environment and the negative
consequences this may have. Ways to reduce, reuse and recycle
resources are becoming more important. In particular, clean water
is becoming a scarce commodity. Therefore, various methods and
devices for purifying water have been published.
[0004] A method for water purification is by capacitive
deionization, using an apparatus having a flow through capacitor
(FTC) to remove ions in water. The FTC functions as an electrically
regenerable cell for capacitive deionization. By charging
electrodes, ions are removed from an electrolyte and are held in
electric double layers at the electrodes. The electrodes can be
(partially) electrically regenerated to desorb such previously
removed ions without adding chemicals.
[0005] The apparatus for removal of ions comprises one or more
pairs of spaced apart electrodes (a cathode and an anode) and a
spacer, separating the electrodes and allowing water to flow
between the electrodes. The electrodes are provided with current
collectors or backing layers and a high surface area material, such
as e.g. carbon, which may be used to store removed ions. The
current collectors may be in direct contact with the high surface
area material. Current collectors are electrically conductive and
transport charge in and out of the electrodes and into the high
surface area material.
[0006] A charge barrier may be placed adjacent to an electrode of
the flow-through capacitor. The term charge barrier refers to a
layer of material which is permeable or semi-permeable for ions and
is capable of holding an electric charge. Ions with opposite charge
as the charge barrier charge can pass the charge barrier material,
whereas ions of similar charge as the charge of the charge barrier
cannot pass the charge barrier material. Ions of similar charge as
the charge barrier material are therefore contained or trapped
either in e.g. the electrode compartment and/or in the spacer
compartment. The charge barrier is often made from an ion exchange
material provided in a membrane. A membrane provided with ion
exchange material may allow an increase in ionic efficiency, which
in turn allows energy efficient ion removal.
SUMMARY
[0007] It is, for example, an object of the invention to provide a
method for preparing an anion exchange membrane, the method
comprising reacting a first monomer with a functional group with a
second monomer to form a copolymer, and reacting the copolymer with
a crosslinker to crosslink the copolymer to form at least part of
the membrane.
[0008] According to an embodiment, there is provided a method of
preparing an anion exchange membrane with anion exchange groups,
the method comprising:
[0009] reacting at least a first monomer comprising vinyl-pyridine
with a pyridine derivative as a functional group with at least a
second monomer comprising styrene to form a substantial linear
copolymer; and
[0010] reacting the copolymer with a crosslinker, the crosslinker
reacting with the pyridine derivative group of the copolymer
crosslinking the copolymer and forming the anion exchange
groups.
[0011] The yield of reacting the vinyl-pyridine with the styrene is
relatively high making the reaction producing the substantially
linear copolymer favorable.
[0012] According to an embodiment there is provided an apparatus to
remove ions, the apparatus comprising: a first and second
electrode; and an anion exchange membrane on the first electrode,
wherein the anion exchange membrane is obtained by crosslinking a
substantially linear copolymer according to a method described
herein.
BRIEF DESCRIPTION OF THE FIGURES
[0013] Embodiments of the invention will be described, by way of
example only, with reference to the accompanying schematic drawings
in which corresponding reference symbols indicate corresponding
parts, and in which:
[0014] FIG. 1 shows a schematic cross-section of an apparatus to
remove ions;
[0015] FIG. 2a shows a detail enlargement of the stack 3 of FIG.
1;
[0016] FIG. 2b shows a detail of FIG. 1;
[0017] FIG. 3 shows an electrode comprising an anion exchange
membrane according to an embodiment; and
[0018] FIG. 4 shows a voltage profile of a stack comprising a
membrane according to an embodiment after 4 h of operation.
DETAILED DESCRIPTION
[0019] FIG. 1 shows a schematic cross-section of an apparatus to
remove ions 1 produced according to, for example, a method
according to an embodiment of the invention, with a part of the
housing removed. In the example the apparatus may comprise twelve
flow through capacitor stacks 3. The flow through capacitor stack 3
may comprise repeating units of a first electrode 4 (see FIG. 2a,
which is an enlargement of a stack), a spacer 8, and a second
electrode 6. The first electrode 4 may comprise one or more first
current collectors 5, which may be bundled together with a first
connector 11 (see FIG. 2b, which is a partial enlargement of FIG.
1). The first connector 11 may be used to clamp first current
collectors 5 together. The second electrode 6 may comprise one or
more second current collectors 9, which may equally be bundled
together on the other side of the apparatus with a second connector
10. The second connector 10 may be used to clamp second current
collectors 9 together.
[0020] The current collectors 5, 9 and the connectors 11, 10 may be
made of the same material e.g. carbon (e.g. graphite) to lower the
electrical resistivity between the current collectors 5, 9 and the
connectors 11, 10. The first connector 11 may have an insert 15
e.g. made from a metal, such as copper. The insert 15 may be
screwed in the first connector 11 so as to help assure low
electrical resistivity between the insert 15 and the first
connector 11. The power terminal 27 is a construction that is
connected to both the power supply and one or more connectors 10,
11. The power terminal 27 may be fixed into the upper and/or bottom
part 22, 24 and/or any other part of the housing. The power
terminal 27 may have a rail e.g. rod 17 made of, for example, metal
e.g. copper to electrically connect the first connector(s) 11 via
the insert(s) 15 to a power source (not shown). The first connector
11 and the insert 15 may have an opening for the rod 17. The insert
15 and the rod 17 may be shielded from the water inside the
apparatus by e.g. resin, glue or paste which functions as a water
barrier. The resin, glue, paste or any other water shielding
material may optionally be applied to the hollow part 19 of the
connector 11 after compression of the stack. To help prevent that
the resin may contaminate the stack 3, one or more rubber rings 12
may be provided in the insert 15. A tray 13 may help manufacturing
one stack 3 and assembling the stacks 3 together in a housing 21 of
the apparatus. Within the housing the stacks 3 may be compressed
between the top and bottom parts 22, 24. A top part 23 of the
housing 21 has a feed-through allowing the rod 17 to make a
connection with a power source. This way electrical charge can
enter the first electrode via the first current collector 5 and
also leave the electrode again, e.g. during regeneration of the
electrodes. Water may be provided to an interior of the apparatus
via an inlet 26. The water is allowed to flow around and through
capacitor stacks 3 and may enter the stacks via the spacers. The
flow through capacitor stack 3 has a hole in the middle of the
stack. In the hole a circular tube 29 is provided and via the space
between the hole and the tube the water may flow to an outlet 30.
The interior of the tube 29 may have a nut 35 and threaded bar 33
which may help to compress the electrodes in the stacks 3 and to
compress the stacks 3 between the upper and bottom parts 22, 24 of
the housing 21.
[0021] Compressing may occur during production of the apparatus, or
optionally during maintenance. By compressing all the stacks at
once it may help assure that the compression force is very similar
or even equal for each stack and at the same time substantially
equally or homogeneously distributed over the surface of the
electrodes.
[0022] During manufacturing of the stack 3 a first electrode
comprising a first current collector 5 may be provided in the tray
13. A spacer may be located on top of the first electrode; and a
second electrode may be put on top of the spacer. Subsequently a
spacer may be put on top of the second electrode followed by
another first electrode. This may be repeated until, for example,
10 first and second electrode units are provided in the stack 3
held by the tray 13, each first electrode separated from a second
electrode with a spacer. Subsequently a connector part 11 may be
located on top of the current collector(s) 5 and a metal insert 15
may be screwed from the other side of the stack 3 through the tray
13 and the first current collectors 5 to fix the stack 3 to the
tray 13.
[0023] The tray 13 and the stack 3 may be connected to the rod 17
of the first power terminal 27 by sliding the insert 15 over the
rod 17 to allow a good electrical contact. The hole in the insert
15 may be of such a size that it allows for good electrical contact
between the insert 15 and the rod 17 and at the same time allow the
insert 15 to slide over the rod 17. The connector 11 may be pressed
on the tray 13 with the current collector(s) 5 in between the
connector 11 and the tray 13 by screwing of the insert 15 in the
connector part 11. To help assure good electrical conductivity
between the connector 11 and the first current collector 5 the
pressure on the connector part 15 and the current collector may be
less than 100 Bar, less than 50 Bar, less than 20 Bar or around 10
Bar.
[0024] Multiple stacks 3 can be connected to the rod 17 and the
stacks 3 may be connected in a similar way to the second connector
10. A force may be exerted on the stacks 3 with the nut 35 and
threaded bar 33 via the upper and bottom parts 22, 24 so as to
compress the first and second electrode in a first direction
substantially parallel to the length of the threaded bar 33 which
is substantially perpendicular to the main surface of the
electrode. The force may exert a pressure on the stack of less than
5 Bar, less than 2 Bar, less than 1 Bar or around 0.5 Bar.
[0025] The first and second connectors 11, 10 allow for movement of
the first and second current collector 5, 9 along the rod 17, 18 in
the first direction such that the current collectors are not
substantially damaged by the compression force on the stack 3. The
movements may be in the order of 0.05 to 10% of the height of the
multiple stacks 3 in the first direction. After enough pressure is
exerted on the stack a resin may be provided along or through the
first and for second connector 11, 10 in the hollow part 19 of the
connectors 10, 11. The resin after hardening fixes the position of
the connectors 10, 11 and may protect the (metal) insert 15 and rod
17 from corrosion.
[0026] FIG. 3 shows schematically the stacking of electrodes,
spacers and membranes in an apparatus to remove ions. The first (4)
and second (6) electrodes are stacked with a spacer (8) and an ion
exchange membrane. The anion exchange membrane (34) may be
positioned between the first electrode (4) and the spacer (8).
During on removal a positive voltage may be applied to the first
electrode. The anion exchange membrane may allow anions to pass
through the membrane towards the first electrode while
substantially blocking the cations.
A Method of Preparing an Anion Exchange Membrane with Anion
Exchange Groups
[0027] In an aspect of the invention, there is provided a method to
prepare a crosslinked linear polymer with anion exchange groups,
the method comprising:
[0028] polymerizing a first monomer with a functional group
selected from the pyridine derivatives with a second monomer
selected from the benzene derivatives to form a copolymer;
[0029] crosslinking the copolymer with a crosslinker; and
[0030] functionalizing the functional group to an anion exchange
group.
The Copolymer
[0031] The copolymer may be prepared by polymerization of at least
two different (co) monomers. The co-monomer may comprise any
carbon-carbon unsaturated compound that can be polymerized in an
addition polymerization reaction. In an embodiment, when a
co-monomer is to be polymerized in an addition polymerization
reaction, it can be an ethylenenically monounsaturated monomer,
e.g. vinyl or allyl compounds. Many of such molecules are readily
available. Examples of co-monomers are vinyl acids, vinyl acid
esters, vinyl aryl compounds (including those with heterocyclic
aryl groups), vinyl acid anhydrides, vinyl amides, vinyl ethers,
vinyl amines, vinyl aryl amines, vinyl nitriles, vinyl ketones,
vinyl aldehydes, terminal alkylenes, and derivatives of these
monomers as well as corresponding allyl variants thereof. The
co-monomer can be hydrophilic or hydrophobic (but hydrophobic
polysiloxane chains may be less desired); anionic, cationic,
uncharged or zwitterionic; it can be a single molecule, oligomeric
or polymeric molecule. In an embodiment, the molecular weight is
lower than 950 Dalton. The co-monomer can be uncharged, negatively,
or positively charged. A co-monomer may also comprise a mixture of
different co-monomers, which may add flexibility, as the polymers
may comprise a variety of different co-monomers with different
chemistries. A single co-monomer may be desired.
[0032] The copolymer may be formed by reacting a first monomer
comprising a pyridine derivative as a functional group with at
least a second monomer comprising a benzene derivative to form a
copolymer. The first monomer with a functional group selected from
the pyridine derivatives may include vinyl pyridines such as:
4-vinylpyridine (CAS: 100-43-6), 3-vinylpyridine (CAS 1121-55-7),
2-vinylpyridine (CAS: 100-69-6), 2-methyl-5-vinylpyridine (CAS:
140-76-1) and/or 5-ethyl-2-vinylpyridine (CAS: 5408-74-2).
[0033] Alternatively for the first monomer a functional
(quaternizable) monomer possessing a ring structure (aliphatic and
aromatic) may be used such as: N-vinyl pyrrolidone;
N-vinylformamide; 4-vinylaniline; N-vinylcarbazole;
1-vinylimidazole; 1-vinyl-1,2,4-triazole;
2-vinyl-4,5-dihydro-1,3-oxazole;
4,4-dimethyl-2-vinyl-4,5-dihydro-1,3-oxazole; and/or
2-N-morpholinoethyl methacrylate. Further, aliphatic non-ring
(linear') functional (quaternizable) monomers (meth)acrylates with
tertiary or secondary amine groups may be used such as:
2-(dimethylaminoethyl) (meth)acrylate; 2-(diethylamino)ethyl
(meth)acrylate; 2-(diisopropylamino) (ethyl)methacrylate;
tert-butylaminoethyl (meth)acrylate; 3-(diethylamino)propyl
(meth)acrylate; 3-(dimethylamino)propyl (meth)acrylate; and/or
(meth)acrylates with quarternary ammonium groups such as:
2-(meth)acryloyloxy)ethyl-trimethylammonium chloride.
[0034] The second monomer comprising a benzene derivative may
comprise a polar styrene derivative such as: 4-tert-butoxystyrene
(CAS: 95418-58-9), 2,4-dimethylstyrene (CAS: 2234-20-0),
2,5-dimethylstyrene (CAS: 2039-89-6), 3-methylstyrene (CAS:
100-80-1), 4-methylstyrene (CAS: 622-97-9), and/or
2,4,6-trimethylstyrene (CAS: 769-25-5).
[0035] A more polar styrene derivative, which is more hydrophilic,
may be used such as: 3,4-dimethoxystyrene (CAS: 6380-23-0),
4-methoxystyrene (CAS: 6380-23-0), 3-hydroxystyrene (CAS:
620-18-8), 4-hydroxystyrene (CAS: 2628-17-3), and/or
4-acetoxystyrene (CAS: 2628-16-2).
[0036] Linear or branched C.sub.1-C.sub.20 acrylates and
methacrylates may be used for the second monomer such as: methyl
(meth)acrylate; stearyl (meth)acrylate; or 2-ethyl hexyl
(meth)acrylate. Methacrylates with alcohol and/or ether groups may
be used as the second monomer such as: 2-hydroxyethyl
(meth)acrylate; 3-hydroxypropyl (meth)acrylate; glycidyl
(meth)acrylates; (meth)acrylic acid esters of (monomethoxy)glycols;
tri(alkyloxy)silylalkylene(meth)acrylates such as:
trimethoxysilylpropyl(meth)acrylate, and/or vinyl ethers and
derivatives such as: methyl vinyl ether and/or vinyl acetate.
[0037] It is possible to apply more than one co-monomer, as this
provides the opportunity to incorporate ion-exchange groups and/or
reactive groups into the copolymer, while it also provides
versatility to tailor the properties of the copolymer. Indeed,
co-monomers may be desirable that provide the polymers with
cations, i.e. anion exchange groups, with anions (i.e. cation
exchange groups), with reactive groups and/or with hydrophilic or
hydrophobic groups. Hydrophilic co-monomers may for example have
alcohol groups, e.g. a co-monomer may be 2-hydroxyethyl
(metha)crylate. Hydrophobic co-monomers are for example styrene or
2-ethylhexyl (meth)acrylate.
[0038] In another embodiment, a co-monomer may comprise reactive
groups that are precursors to ion exchange groups, such as for
example amine groups, particularly tertiary amine groups or
pyridine groups, as upon quaternization with e.g. a halide or
tosylate these reactive groups render quaternary ammonium or
pyridinium anion exchange groups, respectively.
The Crosslinker and the Linear Copolymer
[0039] For the preparation of the crosslinked linear polymer with
ion exchange groups at least a copolymer and a crosslinker may be
provided. The crosslinker may comprise (on average) two reactive
groups, although three or more reactive groups are possible. The
copolymer has reactive groups that enable reaction, forming a
covalent bond, with the crosslinker.
[0040] Control over properties and performance of the crosslinked
copolymer with ion exchange groups may be exerted by choosing the
proper ratio between the copolymer and crosslinker, as this may
determine the molar equivalence between the reactive groups on the
copolymer and crosslinker. Levels of crosslinking can thus be
controlled, as well as the concentration of the ion exchange groups
in the crosslinked copolymer with ion exchange groups. The
crosslinking reaction may be performed with the aid of a solvent
(e.g. an alcohol or non-protic solvent), a reagent (e.g. a
non-nucleophilic base such as diisopropylethyl amine), an
activating agent (e.g. a carbodiimide agent in reactions between
acid and amine reactive groups) and/or a catalyst (e.g. a metal
catalyst in reactions between alcohol and isocyanate). The reaction
conditions may also be varied with regard to temperature,
performing the reaction under an inert gas such as argon or
nitrogen, and/or using a light source as reaction initiator or
stimulus.
[0041] The reactive groups of the crosslinker may react with
reactive groups present in the copolymer. Thus, when one of the
reactive groups of a crosslinker molecule reacts with a reactive
group on a copolymer, the crosslinker molecule is covalently bound
with the copolymer molecule. When the other reactive group of the
crosslinker reacts with another copolymer molecule, forming a
covalent bond with the other copolymer, the crosslinker has formed
a crosslink between two copolymer molecules. Hence, when between
copolymers crosslinks are formed, a crosslinked copolymer may be
formed. Multiple crosslinks between copolymers may occur, and a
network of crosslinked copolymers may be formed. The reactive
groups of the crosslinker and copolymer may be complementary, such
that crosslinkers may not react with each other, and/or copolymers
may not react with each other, such that a crosslinker desirably
reacts with a copolymer. As copolymers may have a large number of
reactive groups, multiple crosslinks between copolymers may be
formed, so that the crosslinker has enabled the formation of a
covalently connected network of copolymers.
[0042] It is possible that to some extent one of the reactive
groups of a crosslinker molecule may react with a reactive group on
a copolymer, while the other reactive group of the same crosslinker
molecule may react with a second reactive group of the same
copolymer, thus forming a covalent connection within one copolymer
that does not contribute to network formation between copolymer
molecules. Such intramolecular reactions, i.e. reactions within a
single copolymer molecule, may be controlled by the varying the
concentration of reactants. Performing the crosslinking process at
high concentration of copolymers may favor the crosslinking process
between copolymer molecules, as the chance of an intermolecular
reaction between copolymers molecules and a crosslinker molecule
increases. Performing the reaction at dilute concentration using a
high amount of solvent increases the occurrence of the
intramolecular reactions, as the chance of intermolecular reactions
between copolymers, of which one already has reacted with a
crosslinking molecule is reduced, and an intramolecular crosslink
may be favored. It is therefore desirable to do the crosslinking
step at a high concentration of the copolymer, using little
solvent, as this may be favorable for efficient crosslinking.
[0043] Linear copolymers may be less soluble, thus reactions are
carried out in less favorable conditions. However polymerizing a
first monomer with a functional group selected from the pyridine
derivatives with a second monomer selected from the benzene
derivatives to form a copolymer may provide a well soluble
copolymer and with regard to intermolecular crosslinking, when such
copolymers are crosslinked, intramolecular crosslinks may more
often be formed.
[0044] Properties of the linear copolymer, such as high solubility,
low solution and melt viscosities and/or high number of reactive
groups per molecule, thus may allow for an easy and efficient
crosslinking step that can result in dense concentrations of ion
exchange groups in the crosslinked membrane with ion exchange
groups. Not much solvent may be needed to dissolve large quantities
of copolymer, so the solution can still have low viscosity which
may make it easier to handle. The crosslinking step may run
smoothly and to high conversions, first in solution when there may
be a high concentration in reactive groups, and after the solvent
has evaporated in the bulk, viscosities can remain relatively low
enhancing the diffusion of reactants.
[0045] The crosslinker or the linear copolymer may comprise an ion
exchange group, such that when the linear copolymer and crosslinker
are reacted a crosslinked polymer with ion exchange groups is
formed.
[0046] As long as a crosslinker and a linear copolymer may have
complementary reactive groups, i.e. they can react with each other
forming crosslinks, such a crosslinker and linear copolymer may be
used. Thus, the complementary reactive groups in the crosslinker
and the linear copolymer may be any combination of two reactive
groups that effectively leads to a covalent bond formation between
the crosslinker and linear copolymer. For example, one may comprise
tertiary amine, pyridine or tertiary phosphine reactive groups,
while the other may have halide, tosylate, mesylate or triflate
reactive groups, such that upon crosslinking, quaternary ammonium,
pyridinium or quaternary phosphonium crosslinks may be formed.
[0047] Accordingly, examples of crosslinkers are diamines,
dihalides, ditosylates, dimesylates, diols, dicarboxylic acids,
di-activated esters, di-vinyl compounds, dianhydrides, particularly
di cyclic anhydrides, di-isocyanates and di-epoxides. Crosslinkers
that may be used include di-cyclic anhydrides, diamines,
dipyridines and dihalides. For amine groups in the crosslinker,
either primary or secondary amines can be used, which are reactive
towards e.g. carboxylic acids and its derivatives or towards
sulfonates and its derivatives. Tertiary amines can also be used
and are desirable as these can generate ion exchange groups upon
reaction with e.g. halides. In case halides are used, the more
reactive halides are desirable, such as activated halides (e.g.
benzyl chlorides), bromides and iodides. Crosslinker molecules may
include, for example, di-cyclic anhydrides such as pyromellitic
dianhydride, EDTA-dianhydride, DTPA-dianhydride,
benzophenone-3,3',4,4'-tetracarboxylic dianhydride, di primary
amines such as diaminobutane and diaminohexane, di secondary amines
such as piperazine and N,N'-dimethyl alkanediamines, di tertiary
amines such as tetramethyl alkanediamines, dipyridines such as
4,4'-bipyridine, or dihalides such as 1,6-diiodohexane,
1,6-dibromohexane, 1,10-dibromodecane.
[0048] In an embodiment of the method for preparing the crosslinked
copolymer with ion exchange groups, an ion exchange group is formed
during the crosslinking step. In an embodiment, the copolymer and
crosslinker comprise reactive groups that are capable of reacting
with each other forming a covalent bond and an ion exchange group.
The ion exchange group that is formed may be an anion exchange
group.
[0049] When the ion exchange group is an anion exchange group, the
reactive group of the copolymer is desirably a pyridine and the
reactive group of the crosslinker may be a halide, tosylate,
mesylate or triflate group. Thus, pyridinium anion exchange groups
may be created when the copolymer and the crosslinker have
reacted.
[0050] The reaction of the linear copolymer with the crosslinker
may result in the formation of an ion exchange group, while
simultaneously crosslinking the linear copolymers, thus preparing a
crosslinked copolymer with anion exchange groups. In addition, or
alternatively, the linear copolymer and/or the crosslinker may
already comprise ion exchange groups. With comprising ion exchange
groups it is meant that the ion exchange groups are covalently
bound to the copolymer, crosslinker and/or crosslinked copolymer.
Alternatively, ion exchange groups may also be covalenty bound to a
crosslinked copolymer already prepared, forming a crosslinked
copolymer with ion exchange groups, although this may be less
desired as it involves an extra step. In any of those cases, a
crosslinked linear copolymer with ion exchange groups is
prepared.
[0051] In a further embodiment, the crosslinker and/or copolymer
may comprise hydrophilic groups and/or hydrophobic groups.
Providing such groups may affect the reaction conditions (e.g.
solvents, reaction kinetics) during the crosslinking step and/or
the properties of the crosslinked copolymer with ion exchange
groups membrane material.
Ion Exchange Group Formation or Activation without Crosslinking the
Copolymer
[0052] Formation of ion exchange groups may also be performed
without crosslinking the copolymer. This way the level of
crosslinking between and within the polymers may be reduced. The
ion exchange capacity of the membrane may not be reduced. The ion
exchange capacity may also be increased without increasing
crosslinking. An advantage of a lower level of crosslinking may be
that the membrane becomes less electrically resistant to ion
transport. This in turn may improve the desalination performance of
the FTC system.
[0053] The formation or activation of ion exchange groups can be
performed by using a group activator. A group activator is a
compound that can react with the copolymer, e.g. with a nitrogen
atom or group at the copolymer, which leads to a charged group in
the copolymer. In an embodiment, the group activator comprises one
reactive group, which is capable of reacting with the copolymer.
The copolymer may have multiple groups that may react with the
group activator and form a covalent bond. The average number of
these reactive groups per copolymer molecule is at least 1, at
least 4, at least 6 or at least 10. An average number of reactive
groups per copolymer may also further describe the copolymer as a
copolymer usually has a heterogeneous mixture of macromolecules. In
an embodiment, the reactive groups of the copolymer that may react
with a group activator are the same reactive groups that may react
with a crosslinker. The reactive group of the group activator may
be the same reactive group of the crosslinker that can react with
the copolymer. The reactive group of the group activator may be
different from the reactive group of the crosslinker, as long as
both can react with the reactive groups of the copolymer. Different
reactive groups for both the crosslinker and group activator may be
contemplated.
[0054] Control over properties and performance of the crosslinked
polymer with ion exchange groups may be exerted by choosing the
proper ratio between the copolymer, group activator and
crosslinker, as this may determine the molar equivalence between
the reactive groups on the polymer, group activator and
crosslinker. The molar ratio between the group activator and the
crosslinker may be any number from 3:1 or even higher or be as low
as 1:3 or even lower.
[0055] The group activator may be reacted with the copolymer
before, during or after the crosslinking step.
[0056] In one embodiment, the crosslinking step is performed with a
limited amount of crosslinker such that not all the reactive groups
of the copolymer available for crosslinking have reacted. In a
post-crosslinking step, the reactive groups of the crosslinked
polymer may be subjected to a reaction with a group activator such
that remaining reactive groups of the copolymer react with the
group activator.
[0057] In one embodiment, the crosslinking step is performed in the
presence of both a crosslinker and a group activator. The ratio
between the crosslinker and the group activator may control the
extent of crosslinking. Having a relatively low amount of
crosslinker may result in a lower extent of crosslinking. It is
understood that not only the ratio of crosslinker and group
activator may determine the extent of crosslinking. For example,
the reactivity of the crosslinker and group activator may also or
alternatively determine the extent of crosslinking. The molar ratio
between the group activator and crosslinker may range from 1:100 to
100:1. The molar ratio between the group activator and the
crosslinker may range from 20:1 to 1:20. The molar ratio between
the group activator and the crosslinker may be 3:1 or higher. The
molar ratio between the group activator and the crosslinker may be
1:3 or lower. It is understood that as long as the amount of
crosslinker in the reaction mixture comprising the crosslinker and
the group activator is sufficient to substantially crosslink the
copolymer, such a ratio may be selected in this embodiment.
[0058] In one embodiment, prior to the crosslinking step the
copolymer is reacted with a group activator. The amount of group
activator is such that at least 2 reactive groups or at least 3
reactive groups remain on average per copolymer for the subsequent
crosslinking step.
[0059] Reaction conditions for reacting a group activator (prior,
during or after crosslinking) with a copolymer may be selected that
are highly similar to the reaction conditions for performing a
crosslinking step.
[0060] The degree of crosslinking can thus be controlled, as well
as the level of ion exchange groups in the crosslinked copolymer.
The group activation reaction may be performed with the aid of a
solvent (e.g. an alcohol or non-protic solvent), a reagent (e.g. a
non-nucleophilic base such as diisopropylethyl amine), an
activating agent (e.g. a carbodiimide agent in reactions between
acid and amine reactive groups) and/or a catalyst (e.g. a metal
catalyst in reactions between alcohol and isocyanate). The reaction
conditions may also be varied with regard to temperature,
performing the reaction under an inert gas such as argon or
nitrogen, and/or using a light source as reaction initiator or
stimulus.
[0061] The reactive group of the group activator may react with
reactive groups present in the copolymer. Thus, when one of the
reactive groups of a group activator molecule reacts with a
reactive group on a copolymer molecule, the group activator
molecule may be covalently bound with the copolymer molecule.
Hence, the ion exchange group is formed without crosslinking of the
copolymer. The reactive groups of the group activator and copolymer
may be complementary, such that group activators may not react with
each other and may not react with the crosslinker, while copolymers
may not react with each other, such that a group activator
desirably reacts exclusively with a copolymer.
[0062] The group activator or the copolymer may comprise an ion
exchange group, such that when the copolymer and the group
activator are reacted a copolymer with ion exchange groups is
formed. In a particular embodiment, a copolymer may have reactive
groups that are ion exchange groups such as e.g. carboxylate or
sulfonate groups, which groups may be converted to amide or
sulfonamide linkages by reaction with amine groups in a group
activator.
[0063] As long as a group activator and a copolymer may have
complementary reactive groups, i.e. they can react with each other
forming an active ion exchange group, such a group activator and
copolymer may be used. Thus, the complementary reactive groups in
the group activator and the copolymer may be any combination of two
reactive groups that effectively leads to a covalent bond formation
between the group activator and copolymer. For example, one may
have alcohol reactive groups, while the other may have carboxylic
acid, carboxylic (activated) ester or anhydride reactive groups to
enable the formation of ester linkages; the other may have
isocyanate reactive groups thus forming urethane linkages; the
other may have halide, tosylate, mesylate or triflate reactive
groups thus forming ether linkages. Furthermore, one of the
reaction components (polymer or group activator) may comprise
primary amine or secondary amine reactive groups, while the other
reaction component may have isocyanate reactive groups (to form
urea linkages), carboxylic acid, carboxylic (activated) ester or
(cyclic) anhydride reactive groups (to form amide linkages),
ethylenenically monounsaturated reactive groups such as
(meth)acrylates, (meth)acryl amides or vinyl derived groups (to
form amine linkages in Michael-type of additions), epoxide reactive
groups (to form an amine alcohol linkage), sulfonate or activated
sulfonate reactive groups (to form sulfon amide linkages), or
halide, tosylate, mesylate or triflate reactive groups (to form
secondary or tertiary amine linkages). Alternatively, one may
comprise tertiary amine, pyridine or tertiary phosphine reactive
groups, while the other may have halide, tosylate, mesylate or
triflate reactive groups, such that upon group activation,
quaternary ammonium, pyridinium or quaternary phosphonium linkages
may be formed.
[0064] Accordingly, examples of group activators are monoamines,
monohalides, monotosylates, monomesylates, alcohols, carboxylic
acids, activated esters, monovinyl compounds, monoisocyanates and
epoxides. Group activators that may be used are monoamines,
monopyridines and monohalides. For amine groups in the group
activator, either primary or secondary amines can be used, which
are reactive towards e.g. carboxylic acids and its derivatives or
towards sulfonates and its derivatives. Tertiary amines can also be
used and are desirable as these can generate ion exchange groups
upon reaction with e.g. monohalides. In case halides are used, the
more reactive halides are desirable, such as activated halides,
bromides and iodides. Group activator molecules are for example
primary amines, secondary amines such as methyl alkaneamines,
tertiary amines such as tetramethyl alkaneamines, pyridines,
monohalides such as alkyl or benzyl halides such as methyl halides,
and/or ethyl halides.
[0065] In another embodiment of the method for preparing the
copolymer with ion exchange groups, an ion exchange group is formed
during the group activation step. In an embodiment, the copolymer
and group activator comprise reactive groups that are capable of
reacting with each other to form a covalent bond and an ion
exchange group. The ion exchange group that is formed may be a
cation exchange group or an anion exchange group.
[0066] When the ion exchange group is an anion exchange group, the
reactive group of the polymer is desirably a tertiary amine, a
pyridine, a guanidine and/or a phosphine group and the reactive
group of the group activator may be a halide, tosylate, mesylate or
triflate group, or the reactive group of the group activator is
desirably a tertiary amine, a pyridine, a guanidine and/or a
phosphine group and the reactive group of the copolymer may be a
halide, tosylate, mesylate or triflate group. Thus quaternary
ammonium, pyridinium, guanidinium or phosphonium anion exchange
groups are created, respectively, when the copolymer and the group
activator have reacted.
[0067] The reaction of the copolymer with the group activator may
result in the formation of an ion exchange group. In addition, or
alternatively, the copolymer and/or the group activator may already
comprise at least one ion exchange group. With comprising ion
exchange groups it is meant that the ion exchange groups are
covalently bound to the copolymer, group activator, crosslinker
and/or crosslinked polymer. Alternatively, ion exchange groups may
also be covalenty bound to a crosslinked polymer already prepared,
forming a crosslinked polymer with ion exchange groups. As long as
a crosslinked polymer with ion exchange groups is prepared or
provided, such a crosslinked polymer with ion exchange groups may
be used.
[0068] In a further embodiment, the group activator and/or polymer
may comprise hydrophilic groups and/or hydrophobic groups.
Providing such groups may affect the reaction conditions (e.g.
solvents, reaction kinetics) during the crosslinking step and/or
the properties of the crosslinked copolymer with ion exchange
groups.
The Ion Exchange Groups
[0069] The ion exchange groups may be dissociable depending on the
pH, but are desirably not pH-dependent, i.e. they do not change
their charge upon pH-changes. Alternatively, the ion exchange
groups may not be pH-dependent over a broad pH-range, for example
from pH 5 to 9, from 3 to 11, from 2 to 12, from 1 to 13 or even
beyond. Ion exchange groups may either be anion exchange groups or
cation exchange groups.
[0070] Anion exchange groups are positively charged and may be
based on nitrogen or phosphor atoms that desirably do not bear any
hydrogen atoms. Examples of anion exchange groups are quaternary
ammonium charges (NR.sub.4), quaternary phosphonium charges (PRA
guanidinium charges, pyridinium charges or charges formed from
nitrogen containing heterocycles other than pyridine, such as for
example imidazoles, triazoles or oxazoles. Most desired may be
pyridinium charges. The so-called strongly basic on exchange groups
(e.g. quaternary ammonium groups) are desired over weakly basic
groups (e.g. secondary or tertiary amines).
The Preparation of the Copolymer
[0071] The copolymer may be prepared by various methods known in
the art and are usually prepared by step-growth methods or by
chain-growth methods. In a typical step-growth method an AB.sub.x
branching monomer is polycondensed (dependent on the availability
of suitable monomers; usually x=2, where x represents the number of
functional groups B in the monomer), where the functional groups A
react with B, and not with other A groups. The B groups also do not
react with each other, and have an equal or similar reactivity
towards A. Side reactions are prevented or are insignificant. The
result is a polymer with a high functionality in B-groups. A number
of variations and modifications of a step-growth method are
possible, and have been developed. For example, in addition to the
AB.sub.X monomer, a multifunctional B.sub.y monomer (where y
represents the number of functional groups B in the monomer), an AB
monomer, or a monomer with only one A-group may be used. In other
frequently used methods, the multifunctional monomers A.sub.2 and
B.sub.y are combined to produce a polymer material. Here, in
principle, crosslinking may occur, but by controlling the
conversion of the polymerization, undesired gelation may be
prevented. Another way to circumvent crosslinking in the reaction
between A.sub.2 and B.sub.y monomers is that one of the B-groups
has a much higher reactivity towards the A-group (and therefore is
in fact a C-group), so that an AB.sub.X monomer is formed in-situ.
Step-growth methods have also been described by the way in which
the monomer is used or applied (see Gao and Yan, Prog. Polym. Sci.,
29, 2004), discriminating between single monomer methodologies
(SMM), double monomer methodologies (DMM) and couple-monomer
methodologies (CMM), where in the latter case the AB.sub.X
branching monomer is formed in situ.
[0072] Step-growth methods are usually polycondensation reactions,
leading to polyesters, polyamides, polycarbonates, polyureas,
polyurethanes, polyethers or polyarylenes, but Michael-type of
additions, i.e. additions where a primary or secondary amine adds
to a double bond (leading to polyamine), or additions of alcohol to
isocyanate (leading to polyurethane) are also possible.
[0073] Chain growth methods that may also be used to prepare
polymers are radical addition polymerization reactions, ring
opening reactions, or anionic or cationic (living) polymerizations.
The radical addition polymerizations may be free radical
polymerizations, or controlled radical polymerizations that are
known in the art, such as nitroxide-mediated radical polymerization
(NMRP), atom-transfer radical polymerization (ATRP) or reversible
addition-fragmentation chain transfer polymerizations (RAFT). Other
controlled chain-growth processes that may be used are
group-transfer polymerizations, ruthenium-catalyzed co-ordinative
polymerizations or ring opening metathesis polymerizations
(ROMP).
[0074] A chain-growth method to prepare polymers may be according
to the so-called self-condensing vinyl polymerization (SCVP),
wherein an AB* branching monomer, in which A is a vinylic group
that is capable of chain-growth vinyl-polymerization and B* is a
group that potentially generates initiating sites for this
vinyl-polymerization, providing the third direction in which the
polymer chain may grow. The AB* branching monomer may be combined
with an A monomer, so that not every monomeric unit is a potential
branching unit. Similarly, in the self-condensing ring-opening
polymerization (SCROP), that is also called ring-opening
multibranching polymerization (ROMBP), an AB* monomer is used,
where A is a heterocyclic ring capable of ring-opening
polymerization, and B* is an initiating group for this ring opening
polymerization. The AB* monomer may be combined with a cyclic A
monomer, so that not every monomeric unit is a potential branching
unit. Glycidol is an example of an AB* monomer that is suitable for
use in SCROP (or ROMBP).
[0075] According to the above, chain growth methods may involve the
use of either vinylic monomers (leading to poly-vinyl type of
polymers) and/or cyclic monomers (typically leading to polyethers
or polyesters). Vinylic monomers can be (meth)acrylates,
(meth)acryl amides, vinyl ethers, vinyl esters or vinyl aryl
monomers. Combinations of these types of vinyl monomers may be
suitable as well. Examples of cyclic monomers are epoxides,
oxetanes, caprolactones or urethanes.
Preparing a Copolymer by an Addition Polymerization Reaction
[0076] The methods for preparation of copolymers described above
are methods describing general ways to prepare copolymer, and are
not limited thereto. It may be of interest to provide for a
versatile method in which the copolymer is synthesized in one
synthetic step, after which the copolymer can be used for the
preparation of the crosslinked polymer with ion exchange groups,
without having to do resort to a post-modification reaction step(s)
on the polymer.
[0077] In one aspect, a copolymer is prepared by a method,
comprising the steps of:
[0078] providing a first monomer with a functional group selected
from the pyridine derivatives,
[0079] providing a second monomer selected from the benzene
derivatives, optionally providing one or more branching
monomers,
[0080] providing an initiator, desirably a free radical
initiator,
[0081] optionally providing a chain transfer agent, and
[0082] reacting the co-monomers, the optional branching monomer(s),
the initiator and the optional chain transfer reactant to form a
copolymer.
[0083] In one embodiment, the reaction step may involve an addition
polymerization reaction or, desirably, a free-radical
polymerization reaction. In this method, the chemistry of the
reactants (i.e. co-monomers, initiator, (optional) branching
monomer and/or (optional) chain transfer agent) and the reaction
conditions may be selected such that crosslinking reactions may be
prevented between copolymer molecules that are being formed during
the reacting step (i.e. preventing gelation or solidification).
[0084] In an embodiment, the branching monomer comprises at least
two vinyl groups, and the co-monomer comprises one vinyl, where the
vinyl groups are suitable for addition polymerization. In an
embodiment, the product is a poly(4 vinyl pyridine-co-styrene).
[0085] The preparation methods and reactants (e.g. branching
monomer, co-monomer, initiator and/or chain transfer agent)
described below are versatile in the sense that the copolymer may
be prepared from readily available monomers and reactants, and that
it can be tailored with respect to its properties by simply varying
the used amounts of the (optional) branching monomer, the
co-monomer(s), the initiator and the (optional) chain transfer
agent. The extent of branching of the copolymer may be controlled
by adjusting the amount of branching monomer in the polymerization
reaction, while the use of the types and amounts of co-monomers may
determine the type and amount of ion exchange groups and/or
reactive groups in the polymer. Care may be taken to select a ratio
between the chain transfer agent and the branching monomer such
that gelation is prevented during the polymerization reaction,
while still generating a copolymer of a substantial molecular
weight, e.g. with copolymer molecules with a number average
molecular weight (Mn) in the range of 250 Dalton to 100,000 Dalton
(see for example O'Brien, Polymer, 41, 2000, 6027-6031). All
branched monomers, co-monomers, initiators and/or chain transfer
agents may comprise groups, or may transfer groups, such that the
copolymer formed may comprise these groups.
[0086] When co-monomers are combined, for instance to provide for
different chemistries in the copolymer, e.g. see example Reaction
scheme 1 wherein 4-VP provides for a pyridine and HEMA/MMA provides
for hydrophilic groups, one co-monomer may have a high reactivity
with the CTA. Because of this high reactivity, a side product may
be formed when the CTA and this co-monomer react. When this is the
case, more of the CTA and more of the co-monomer may be used to
compensate for the loss of reactants in the side product. For
example, the co-monomer 4-vinyl pyridine can readily form a
thioether side product with a linear primary thiol CTA. For
instance, the amounts of CTA and/or co-monomer may be increased in
the reaction mixture, whereas the amount of CTA and/or co-monomer
incorporated is similar (see Table 1 and Table 2, compare e.g. 12A
with 21).
[0087] In the reaction mixture, the amount of co-monomer(s) used is
desirably in the range of 40 mol/mol % to 98 mol/mol %, and the
amount of branching monomer(s) and/or CTA is desirably from 2
mol/mol % to 50 mol/mol %. The initiator can be used in amounts
varying from 0.01 mmol/mol.degree./0 to about 5 mol/mol %, relative
to the amount of co-monomer(s), branching monomer(s) and CTA
reactants. When higher molar percentages of initiator are used, the
application of inhibitor additives or retarding agents (e.g.
benzoyliminoacetate) may be considered. However, inhibitors or
retardants may be avoided when about 1 mmol/mol % of initiator is
used.
[0088] The radical polymerization reaction may be performed using
reaction conditions known to the skilled person, selecting a
solvent (e.g. toluene or ethanol), concentration of reactants and
monomers (i.e. solids), temperature and addition method of
monomers, reactants and/or solvent as are known in the art for
polymerization reactions. Desirably, the reaction is performed in
alcohols such as ethanol, with concentrations ranging between 3 w/w
% and 30 w/w % in solids or between 10 w/w % and 25 w/w %, at
temperatures between 60.degree. C.-90.degree. C. In an embodiment,
all monomers, reactants and solvents are premixed before the start
of the reaction. Prior to a radical polymerization, the reaction
mixture is desirably freed of oxygen, for example by purging it
with an inert gas such as nitrogen.
[0089] The copolymer may next be isolated. The copolymer may for
instance be isolated by precipitation or stirring in a non-solvent
for the copolymer. For this purpose the solvent in which the
reaction was carried out may first be evaporated, prior to addition
of the non-solvent. In the precipitation step by-products or
less-preferred product fractions of low molecular weight may be
removed.
[0090] Alternatively, the reaction mixture comprising the copolymer
may also be directly used for the crosslinking reaction, forming a
crosslinked copolymer with ion exchange groups.
The Optional Branching Monomer
[0091] A branching monomer may be a molecule comprising two vinyl
groups (i.e. an ethylenenically diunsaturated monomer). The
branching monomer may also comprise more than two vinyl groups.
These vinyl groups can be polymerized in an addition polymerization
reaction and may be provided in relatively low amount compared to
the first monomer with a functional group selected from the
pyridine derivatives and the second monomer selected from the
benzene derivatives to provide some amount of branching in the
polymer. Many of such molecules are readily available, or may be
prepared by reacting any di- or multifunctional molecule with a
suitably reactive vinylic reactant. Examples include di- or
multivinyl esters, di- or multivinyl amides, di- or multivinyl aryl
compounds (including those with heterocyclic aryl groups), and di-
or multivinyl alkyl/aryl ethers. The branching monomer may be
hydrophilic or hydrophobic (but hydrophobic polysiloxane chains may
be less desired). The branching monomer can be either uncharged or
negatively or positively charged. The branching monomer may be a
single molecule, an oligomeric molecule or a polymeric molecule.
The branching monomer may also comprise a mixture of different
branching monomers. The molecular weight of a branching monomer may
be lower than 950 Dalton. The branching monomer may desirably be
uncharged, and desirably a single compound.
[0092] Branching monomers include, but are not limited to, divinyl
aryl monomers such as divinyl benzene (DVB); (meth)acrylate
diesters such as alkylene di(meth)acrylates such as ethylene glycol
di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butylene
glycol di(meth)acrylate; oligo alkylene glycol di(meth)acrylates
such as tetraethyleneglycol di(meth)acrylate, poly(ethyleneglycol)
di(meth)acrylate, poly (propyleneglycol) di(meth)acrylate; divinyl
(meth)acrylamides such as methylene bisacrylamide; divinyl ethers
such as poly(ethyleneglycol)divinyl ether; and tetra- or
tri-(meth)acrylate esters such as pentaerythritol tetra
(meth)acrylate, trimethylolpropane tri(meth)acrylate or glucose di-
to penta (meth)acrylate. Desirable branching monomers may be
divinyl benzene, .alpha.,.omega.-alkylene di(meth)acrylates,
divinyl (meth)acrylamides, ethylene glycol di(meth)acrylate,
1,4-butylene glycol di(meth)acrylate and/or methylene
bisacrylamide.
[0093] In an embodiment, the branching monomer is a
di(meth)acrylate, a bisacrylamide, 1,4-butanediol dimethacrylate or
methylene bisacrylamide.
The Initiator and the Chain Transfer Agent
[0094] The initiator is a molecule that can initiate a
polymerization reaction. In case the polymerization reaction is a
(free)-radical polymerization reaction, the initiator may be a
(free)-radical initiator which may be any molecule known to
initiate such a reaction, such as e.g. azo-containing molecules,
peroxides, persulfates, redox initiators, and benzyl ketones. Such
initiators may be activated via thermal, photolytic or chemical
means. Examples of (free)-radical initiators are
2,2'-azobisisobutyronitrile (AIBN), azobis(4-cyanovaleric acid),
benzoyl peroxide, cumylperoxide, 1-hydroxycyclohexyl phenyl ketone
and hydrogenperoxide/ascorbic acid. The so-called iniferters may
also be considered as initiators. AIBN may be desirable as a
(free)-radical initiator.
[0095] The chain transfer agent or reactant is a molecule that can
control, limit and reduce the molecular weight during radical or
free-radical polymerization via a chain transfer mechanism, as is
known in the art. For example, a chain transfer agent in a radical
polymerization reaction can react with the group of the polymer
comprising the radical, such that the radical is transferred to the
chain transfer agent. The result is that the chain transfer agent
comprises the radical, and the polymerization of the group of the
polymer that previously comprised the radical has stopped. The use
of a chain transfer agent may prevent that the polymerization
reaction will result in crosslinking reactions and gel formation.
The chain transfer agent in a radical polymerization reaction may
be any thiol-containing molecule and can be mono- or
multifunctional. Examples of suitable thiols are linear or branched
C2-C18 alkyl thiols such as dodecane 1-thiol, thioglycolic acid,
thioglycerol, cysteine and cysteamine, 2-mercaptoethanol,
thioglycerol, dithiothreitol (DTT) and ethylene glycol mono- (and
di-)thio glycollate. Thiols may in addition bear reactive and/or
ion exchange groups, such as carboxylic acids, amines or alcohols.
Apart from thiols, other agents that can stabilize a radical and/or
that are known to limit the molecular weight in a free-radical
addition polymerization may be considered. For example, hindered
alcohols, organic complexes of cobalt are known as chain transfer
catalysts, such as bis(borondifluorodimethyl-glyoximate) (CoBF) or
cobalt oximes, and reversible addition fragmentation transfer
(RAFT) agents such as xanthates, dithioesters and dithiocarbonates,
or alkyl halides. A desirable chain transfer agent is a thiol, an
organic thiol, or an organic linear or branched C6-C20 alkyl
thiol.
An Ion Exchange Membrane Comprising the Crosslinked Copolymer Ion
Exchange Groups
[0096] A crosslinked copolymer with ion exchange groups obtainable
or obtained by the methods as described herein may be provided.
Such a crosslinked copolymer with ion exchange groups may be in the
form of a sheet. An embodiment of the invention provides for an ion
exchange membrane comprising the crosslinked copolymer containing
ion exchange groups, that desirably is prepared as a sheet.
[0097] The crosslinked polymer may have gel like or solid like
properties. The crosslinking reaction may be performed in a coating
or a film, such that a sheet of crosslinked copolymer is formed.
The reactive film may be prepared by any processing technique
feasible, such as for example by spraying a solution that contains
both the copolymer and the crosslinker onto a surface, or by
applying such a solution onto a substrate by any coating technique,
e.g. by a so-called doctor blade, roll to roll, knife over edge or
slot dye coating technique.
[0098] The crosslinking reaction may be performed directly onto the
surface or substrate of choice, for example onto a specific support
layer or onto an electrode. By crosslinking the copolymer on the
electrode the strength of the membrane and the electrode may be
increased. The increased strength may be used to make the electrode
and or the membrane thinner. Furthermore, stack assembly may become
easier because fewer layers may need to be stacked during assembly
because two layers are already integrated with each other. The
crosslinking reaction on the electrode may help assure that there
is intimate contact between the electrode and the membrane. This
way air and/or water pockets between the electrode and the membrane
may be avoided. The crosslinker and copolymer may be provided
directly onto the electrode, whereby the membrane network is formed
in situ. The crosslinker and copolymer may be partially penetrating
into the electrode to enhance intimate contact between membrane and
electrode. This may be done by impregnating the electrode with a
solvent, e.g. water and casting the membrane casting solution onto
the electrode, whereby the casting solution is capable of wetting
the electrode surface (containing the electrode solvent, e.g.
water). During cross linking the membrane onto the electrode, the
membrane could even be partially crosslinked with the electrode,
which would lead to a stronger bond between electrode and membrane
than when the bond is only by a physical attraction force. A strong
bond between membrane and electrode may help in reducing a
potential swelling of the membrane along the electrode surface,
once the membrane is brought in contact with water. In addition,
the strong bond may also help in preventing that the membrane
becomes loose and/or delaminated from the electrode surface.
[0099] In a further embodiment the crosslinking may be done
partially with the spacer that is applied against the membrane. By
doing the crosslinking onto the spacer, there will be intimate
contact between the membrane and the spacer and the spacer and
membrane layers will be integrated into one layer, which will make
stack assembly easier.
[0100] The crosslinking reaction may be performed to prepare small
sphere-like shaped crosslinked copolymer particles (e.g.
microspheres), for example by performing the crosslinking in small
droplets, which may be used to prepare e.g. a paste, such that the
crosslinked copolymers may be applied to irregular surfaces or
shapes.
[0101] The crosslinking step may at first instance be done
partially in a reactor, and may subsequently be transferred to the
object, substrate or surface of choice, where the reaction may be
completed. Since during the crosslinking step the viscosity of the
reaction mixture may increase, due to the crosslinks that are
formed, the properties of the reaction mixture may change from a
liquid to a more viscous, paste like mixture which may make it
convenient to apply the reaction mixture to a surface, or a mold,
which may even have an irregular surface. Hence, it may be
advantageous to transfer the reaction mixture during the reaction
to an object, substrate or surface of choice, where the reaction
will be completed.
[0102] In another aspect, an ion exchange membrane is provided
which comprises sheets of crosslinked copolymer with ion exchange
groups, wherein the thickness of the sheets of crosslinked
copolymer with ion exchange groups is less than 200 micrometers,
less than 100 micrometers, less than 60 micrometers or less than 30
micrometers.
[0103] The concentration of the ion exchange groups, either
cationic or anionic, in the crosslinked copolymer with ion exchange
groups is between 0.2 and 6 mmol per gram, between 0.8 and 5 mmol
per gram, between 1.4 and 4 mmol per gram, between 2 and 3 mmol per
gram or between 2.2 and 2.7 mmol per gram. These numbers refer to a
dry crosslinked copolymer with ion exchange groups. In an
embodiment, the crosslinked copolymer with ion exchange groups
comprises between 25% and 95%, between 40% and 85%, or between 55%
and 80% by weight of the copolymer. The concentrations of ion
exchange groups in mmol/g of dry crosslinked copolymer with ion
exchange groups, and percentages by weight of copolymer in the dry
crosslinked copolymer with ion exchange groups may e.g. be
calculated from the amounts of copolymer and crosslinker that have
been used in the preparation of the crosslinked copolymer membrane
material.
[0104] Furthermore, the crosslinked copolymer with ion exchange
groups material may comprise additional hydrophilic groups, such as
for example alcohol or amide groups, and/or additional hydrophobic
groups, such as for example C.sub.8 or higher alkyl or alkylene
groups, where these hydrophilic and/or hydrophobic groups may
originate from the crosslinker and/or from the copolymer. In this
way, the crosslinked copolymer with ion exchange groups may be more
compatible with water and/or may improve the electrical conductive
properties of the crosslinked copolymer with ion exchange groups
and/or may improve the performance of the membrane material.
[0105] The (sheets of) crosslinked copolymer with ion exchange
groups, that may be used for ion exchange membranes, may have
little or no curling or delamination when after preparation they
are brought in contact with water and also at the same time may
show little swelling. Furthermore, advantageous permselectivities
may be obtained with crosslinked copolymers with ion exchange
groups. As is described in the examples, for instance,
permselectivities higher than 90% may be obtained with sheets in
the range of 40 micrometers (see example 17). Permselectivity or
permeability selectivity, is defined as the percentage of cations
or anions, of the total amount of ions that may be taken up by a
membrane, in this case a membrane comprising the crosslinked
copolymers with ion exchange groups. When a membrane has a
permselectivity of 100% for anions, this means that 100% of the
ions may be taken up by the membrane are anions. When the
permselectivity is reduced e.g. by 5% to a permselectivity of 95%,
this means that 95% of the ions that are taken up by the membrane
are anions, and 5% are cations. Please note that for ion exchange
membranes, especially for those applied in FTCs, every percent
increase in permselectivity may be very valuable, with 100% being
the maximum selectivity achievable. Also, a low resistance, as low
as 5 ohm*cm.sup.2, or even as low as 1.5 ohm*cm.sup.2, may be
desirable for the prepared sheets of crosslinked copolymers with
ion exchange groups.
EXAMPLES
Experimental Details
[0106] All solvents were of AR quality if not stated otherwise and
were purchased from commercial sources (Biosolve or Acros).
Petroleum ether (boiling point range 60-80.degree. C.) was
purchased from ABCR. Deuterated solvents were purchased from
Cambridge Isotope Laboratories and were dried over molsieves. The
monomers 2-hydroxyethyl methacrylate (HEMA) (97%), methyl
methacrylate (MMA) (99%) and the branching monomer divinylbenzene
(DVB) (70-85%) were purchased from Aldrich. DVB consists of a
mixture of 1,4-divinylbenzene and 1,3-divinylbenzene and contains
significant amounts of ethylvinylbenzene and diethylbenzene. The
chain transfer agent 1-dodecane thiol (99%), the monomers 4-vinyl
pyridine (4-VP) (95%) and styrene (99.5%), the initiator
2,2'-azo-bis(2-methylpropionitrile) (AIBN) (98%) were purchased
from Acros. .sup.1H-NMR spectra were recorded in CDCl.sub.3 on a
Varian 400 MHz or 200 MHz NMR spectrometer, where .sup.1H-NMR
chemical shifts are given in ppm, and were determined using
tetramethylsilane (TMS) as internal standard (0 ppm). Infrared
spectra of samples were recorded on a Perkin Elmer Spectrum One
1600 ATR FT-IR spectrometer. Wavenumbers are given in cm.sup.-1.
GPC (or SEC) chromatograms of the polymers were measured using 10
mM of LiBr in DMF as eluent, applying a 1 mL/min eluent flowrate, a
sample concentration of 2 mg/mL in 10 mM of LiBr DMF and an
injection volume of 20 microL. A Polymer Laboratories PL-GPC50 Plus
Integrated GPC system was used, equipped with a Polymer Standards
Service (PSS) Gram analytical linear M column (dimensions
8.times.300 mm, particle-size 10 micro-m, mass range: 500-1000000
Da) that was operated at 50.degree. C. and applying refractive
index (RI) detection. Calibration was performed with
polyethyleneoxide reference standards. Elemental analysis was
performed on a Perkin Elmer 2400 machine, where elemental contents
are given in weight percentages. DSC was performed on a TA Q2000
instrument, where monitored samples are kept under a nitrogen
atmosphere. Glass transition temperatures (Tg) are given as
observed during the second heating run using a heating rate of
20.degree. C./min.
The Preparation of the Copolymers
[0107] Copolymers were synthesized in addition polymerization
reactions, Methacrylate/4-vinyl pyridine based copolymers (see
Scheme 1) as well as styrene/4-vinyl pyridine based copolymers (see
Scheme 2) were prepared. Also a styrene/4-vinyl pyridine
hyperbranched copolymer with divinyl benzene as branching monomer
was prepared (see Scheme 2).
##STR00001##
##STR00002##
For the methacrylate based linear polymers with pyridine groups
(Scheme 1), 2-hydroxyethyl methacrylate (HEMA) or methyl
methacrylate (MMA) were used as comonomers. These monomers differ
in polarity, thus enabling control of the polarity of the
copolymer. Besides methacrylates, styrene was selected as comonomer
with 4-VP, and the introduction of divinylbenzene enables the
synthesis of hyperbranched copolymers. Similar reaction conditions
were used for all synthetic examples, with 1 molar-% of AIBN
radical initiator with respect to the total amount of reactive
vinylic groups in the polymerization. Ethanol was used as solvent.
Dodecane thiol was used as chain transfer agent in all examples,
which may result in the formation of a thioether side product, see
also A. R. Katrizky et al., J. Org. Chem., 1986, 51, 4914.
Temperatures were around 70.degree. C. Polymers were purified by
washing with heptane or petroleum ether.
Example 1
Linear Copolymer 10B
[0108] 4-Vinyl pyridine (7.91 g, 71.43 mmol), 2-hydroxyethyl
methacrylate (3.57 ml, 28.57 mmol), n-dodecane thiol (10.33 ml,
42.86 mmol) and AIBN (167 mg, 1 mmol) were dissolved in ethanol (67
ml) in a 3-neck 250 ml round-bottom flask under stirring. The
beige, clear solution was purged with argon for 1 h while stirring.
A reflux condenser was fitted and the reaction mixture was then
stirred and heated at an oil bath temperature of 75.degree. C. for
15 h, and was kept under an argon atmosphere. The solvent was
evaporated in vacuo and the orange residual syrup redissolved into
ethanol (15 ml) and subsequently precipitated into an ice-cold
mixture of heptane (200 ml) and diisopropyl ether (100 ml) during
which a beige slurry formed. The slurry was filtered over a glass
filter and the residue was washed twice with an ice-cold mixture of
heptane (33 ml) and diisopropyl ether (17 ml). Overnight drying of
the residue in vacuum yielded the reference linear copolymer 10B as
a light-yellow solid (7.19 g, 36%). .sup.1H-NMR (CDCl.sub.3 and
CD.sub.3OD): .delta.=8.42 (pyridine, broad peak (bp)), 7.08
(pyridine, bp), 4.08 (ester, bp), 3.78 (ester/alcohol, bp), 3.53
(ester/alcohol, bp), 2.5-0.4 (multiple signals, bp), 1.25 (alkyl
tail CH.sub.2-groups), 0.88 ppm (triplet (t), .sup.3J (H, H)=6.3
Hz, alkyl tail CH.sub.3-group). FT-IR (ATR): v (cm.sup.-1)=3233,
2925, 2854, 1721, 1598, 1558, 1454, 1417, 1386, 1220, 1183, 1145,
1083, 1070, 1026, 1003, 994, 897, 820, 755; GPC (DMF-LiBr): Mn=0.2
kg/mol, Mw=0.3 kg/mol, PDI=1.7; Elemental analysis: C, 67.23; H,
7.88; N, 5.58. Number of pyridine groups as derived from .sup.1H
NMR data: 4.2 mol/kg linear copolymer. T.sub.g=39.degree. C.
Example 2
Linear Copolymer 22A
[0109] 4-Vinyl pyridine (11.88 g, 107.1 mmol), methyl methacrylate
(4.65 ml, 42.9 mmol), dodecane thiol (15.5 ml, 64.3 mmol) and AIBN
(249 mg, 1.5 mmol) were dissolved in ethanol (100 ml) in a 3-neck
250 ml round-bottom flask under stirring. The beige, clear solution
was purged with argon for 1 h while stirring. A reflux condenser
was fitted and the reaction mixture was heated at an oil bath
temperature of 70.degree. C. under argon and stirring for 16 h. The
solvent was evaporated in vacuo and the orange residual syrup mixed
with heptane (100 ml). This mixture was heated to reflux under
stirring to give a beige emulsion. After 0.5 h, the emulsion was
allowed to reach room temperature during which time the orange
material settled and an orange, clear supernatant formed. The
latter was decanted and the residue was mixed with heptane (100 ml)
and subsequently heated to 80.degree. C. Stirring of the viscous
mixture was performed for 10 minutes after which the mixture was
allowed to reach room temperature. An almost colorless, turbid
supernatant formed which was decanted and the beige residue was
collected, dried under vacuum at room temperature and subsequently
mixed with pentane (100 ml) to give a beige suspension upon
grinding and stirring. The suspension was allowed to settle, so
that a supernatant formed that was then decanted. The residue was
collected and dried under vacuum at room temperature in the
presence of KOH to give linear copolymer 22A as a beige powder
(7.85 g, 27%). .sup.1H-NMR (CDCl.sub.3): .delta.=8.46 (pyridine,
bp), 6.87 (pyridine, bp), 3.54, 3.35 and 2.91 (ester/alcohol, bp),
2.5-0.4 (multiple bp), 1.24 (alkyl tail CH.sub.2), 0.86 ppm (t,
.sup.3J (H, H)=6.1 Hz, alkyl tail CH.sub.3); FT-IR (ATR): v
(cm.sup.-1)=3423, 3024, 2988, 2925, 2853, 1725, 1597, 1557, 1448,
1416, 1358, 1219, 1196, 1134, 1069, 993, 820, 754; GPC (DMF-LiBr):
Mn=0.7 kg/mol, Mw=1.5 kg/mol, PDI=2.1; Elemental analysis: C,
71.74; H, 7.79; N, 7.46. Number of pyridine groups as derived from
.sup.1H NMR data: 5.5 mol/kg linear copolymer. T.sub.g=41.degree.
C.
Example 3
Linear Copolymer 112
[0110] 4-Vinyl pyridine (6.79 g, 61.3 mmol), styrene (12.85 g, 123
mmol), dodecane thiol (0.160 g, 0.77 mmol) and AIBN (0.308 g, 1.84
mmol) were dissolved in ethanol (60 ml) in a 3-neck 100 ml
round-bottom flask under stirring. The beige, clear solution was
purged with argon for 2 h while stirring. A reflux condensor was
fitted and the reaction mixture was heated at an oil bath
temperature of 72.degree. C. under argon and stirring for 26 h. The
solvent was evaporated in vacuo and the orange, sticky residue was
mixed with heptane (50 ml) in a 100 ml flask and heated at reflux
for 2 hours under mechanical stirring. The mixture was allowed to
reach room temperature and subsequently the heptane phase was
decanted. The resulting beige, sticky residue was dissolved into
chloroform (25 ml) and precipitated into well-stirred petroleum
ether (250 ml). The petroleum ether phase was decanted and the
beige residue dried in a vacuum oven at 30.degree. C. overnight
yielding copolymer 112 as a beige, glassy powder (17.8 g, 94%).
.sup.1H-NMR (CDCl.sub.3): .delta.=8.25 (pyridine, bp), 7.08
(styrene and pyridine, bp), 6.45 (styrene, bp), 2.1-1.0 ppm
(multiple bp); FT-IR (ATR): v (cm.sup.-1)=3061, 3025, 2921, 2851,
1946, 1870, 1596, 1557, 1493, 1452, 1414, 1373, 1328, 1219, 1182,
1155, 1068, 1028, 993, 907, 819, 756, 698; GPC (DMF-LiBr): Mn=3.5
kg/mol, Mw=10 kg/mol, PDI=2.9; Number of pyridine groups as derived
from .sup.1H NMR data: 3.5 mol/kg linear copolymer. The copolymer
has a glass transition temperature between 60 and 80.
T.sub.g=76.degree. C. The yield of the copolymer reaction was
94%.
Example 4
Hyperbranched Copolymer 116
[0111] 4-Vinyl pyridine (7.06 g, 63.8 mmol), styrene (13.21 g, 126
mmol), dodecane thiol (12.95 g, 62.7 mmol), divinylbenzene (0.945
g, 6.2 mmol) and AIBN (0.339 g, 2.0 mmol) were dissolved in ethanol
(69 ml) in a 3-neck 250 ml round-bottom flask under stirring. The
beige, clear solution was purged with argon for 1 h while stirring.
A reflux condensor was fitted and the reaction mixture was heated
at an oil bath temperature of 71.degree. C. under argon and
stirring for 25 h. The solvent was evaporated in vacuo and the
brownish, sticky, viscous syrup was mixed with petroleum ether (150
ml) in a 250 ml flask after which immediately a beige, sticky
precipitate formed. The petroleum ether phase was decanted and the
beige, sticky residue was mixed with petroleum ether (100 ml) and
heated at reflux (oil bath=100.degree. C.) for 1 hour. Manual
stirring with a spatula was applied. The mixture was allowed to
reach room temperature and subsequently the petroleum ether phase
was decanted. The resulting beige, sticky residue was mixed with
petroleum ether (100 ml) and heated at reflux (oil bath=105.degree.
C.) for 1 hour. Manual stirring with a spatula was applied. The
mixture was allowed to reach room temperature and subsequently the
petroleum ether phase was decanted. The beige residue was dried in
a vacuum oven at 60.degree. C. overnight yielding copolymer 116 as
a beige, glassy powder (6.2 g, 19%). .sup.1H-NMR (CDCl.sub.3):
.delta.=8.24 (pyridine, bp), 7.08 (styrene and pyridine, bp), 6.50
(styrene, bp), 2.7-1.0 (multiple bp), 1.26 (alkyl tail CH.sub.2),
0.88 ppm (triplet (t), .sup.3J (H, H)=6.2 Hz, alkyl tail
CH.sub.3-group); FT-IR (ATR): v (cm.sup.-1)=3060, 3025, 2922, 2852,
1946, 1873, 1804, 1596, 1557, 1492, 1452, 1414, 1369, 1328, 1219,
1181, 1155, 1068, 1023, 993, 907, 820, 757, 697; GPC (DMF-LiBr):
Mn=1.1 kg/mol, Mw=7.3 kg/mol, PDI=6.8; Number of pyridine groups as
derived from .sup.1H NMR data: 2.4 mol/kg hyperbranched copolymer.
T.sub.g=67.degree. C. The yield of the copolymer reaction was
19%.
[0112] The relative molar amounts of the quaternizable monomer
4-vinyl pyridine, the comonomer and reactants that were used in
Examples 1-4 are compiled in Table 1. Table 1 also contains the
molar composition of the product copolymers, which was determined
by .sup.1H-NMR spectroscopy.
TABLE-US-00001 TABLE 1 Applied molar compositions of the reaction
mixtures and molar compositions of the isolated copolymers. Example
dodeca- Entry 4-VP HEMA MMA styrene DVB nethiol Applied molar ratio
of the monomers in the reaction mixture 1 .sup. 10B 25 10 -- -- --
15 2 .sup. 22A 25 -- 10 -- -- 15 3 112 10 -- -- 20 -- 0.12 4 116 10
-- -- 20 1 10 Molar ratio of the monomeric units in the copolymers
1 .sup. 10B 10 6.7 -- -- -- 2.1 2 .sup. 22A 10 -- 4.8 -- -- 1.4 3
112 10 -- -- 17 -- 0 4 116 10 -- -- 25 ? 2.7 Note: The amount of
DVB in polymer 116 could not be derived from its .sup.1H-NMR data.
The amount of AIBN was always 1 mol-% compared to vinyl groups
(note that DVB possesses two vinyl groups). Abbreviations are
explained in Schemes 1 and 2.
Membrane Preparation
[0113] Poly(4-vinyl pyridine-co-styrene) linear copolymer 112 from
example 3 was received as a dry powder. The polymer ratio between
4-vinyl pyridine and styrene was 1:1.63. Copolymer was dissolved in
N-butyl acetate (Sigma-Aldrich) to obtain 45% (by weight) solution.
Membranes can be crosslinked by using dihalides (alkyl, alkenyl,
alkynyl and aryl dihalides).
[0114] P(4-VPcS) was tested with 1,6-diiodohexane,
1,5-dibromopentane, 1,6-dibromohexane and 1,10-dibromodecane. To
activate ion exchange groups without crosslinking monohalides can
be used. For pilot experiments 1,6 diiodohexane was chosen. Amount
of 1,6-diiodohexane (98% stabilized with copper, Alfa Aesar) was
added in order to achieve 100% crosslinking, solution was mixed for
6 minutes after the crosslinker was added. Membranes were casted on
a glass plate. For full scale experiments they were casted with a
thickness set on applicator to 120 .mu.m. Casting was performed by
automatic applicator (Zehnter ZAA 2300, speed set to 1 mm/s).
Casted films were dried in the oven for 24 h at approximately
50.degree. C. then soaked off the glass plates, put into 0.05M KCl
solution for 4 days (to let membranes swell and exchange
counter-ions). Next step was to cut membranes to proper dimension
(16.times.16 cm) in order to put them in the CapDI system.
Subsequently membranes were tested in full scale stack at CC for 3
days. Before and after constant current test small samples of the
membranes were taken to characterize them (resistance,
permselectivity, swelling and IEC).
Calculations of Amount of Crosslinker and Theoretical IEC
[0115] Amount of crosslinker = E = A * B 100 * C * D 200 * Mw 1
1000 ##EQU00001## IEC theoretical = A * B * C A * B + E - F = 2.62
mmol g ##EQU00001.2##
[0116] Where:
[0117] A=Amount of polymer solution [g];
[0118] B=Polymer concentration [%];
[0119] C=Pyridine groups per gram of dry polymer [mmol/g];
[0120] D=Crosslinking percentage [%];
[0121] E=Amount of crosslinker [g];
[0122] F=Counter ion weight correction (NO.sub.3.sup.- form)
[g];
[0123] Mw1=Molar weight of crosslinker (337.97, 1,6
Diiodohexane).
P(4-VPcS) Membrane Performance as a Function of Membrane
Thickness
[0124] Membrane resistance was measured at 2M NaCl by direct
current method and permselectivity was measured by membrane
potential method (0.5M/0.05M KCl). IEC capacity was measure by
exchanging counter ions. All methods are described in more details
in Piotr Dlugolecki et. al. Journal of Membrane Science 319 (2008)
214-222.
[0125] Membrane thickness was investigated in order to evaluate
influence on the membrane resistance, membrane selectivity and
membrane mechanical stability.
TABLE-US-00002 TABLE 1 Membrane performance as a function of
membrane film thickness Casting Wet thickness thickness Resistance
Selectivity [.mu.m] [.mu.m] [.OMEGA. cm.sup.2] [%] 60 19 1.00 97.8
90 25 1.22 97.4 120 41 1.51 98.2 180 59 2.12 98.4 240 68 2.56
97.9
[0126] P(4-VPcS) membrane resistance is a function of membrane
thickness. The lowest resistance values were achieved for 60 and 90
microns casted samples. Selectivity for all samples thickness
remains stable. For comparison, the data with respect to example 4
hyperbranched copolymer 116 are depicted below. The electrical
resistance is much higher than the linear copolymer 112, making the
linear copolymer desirable.
TABLE-US-00003 Hyperbranched copolymer 116 (pyridine:styrene 1:2.5)
Pyridine content 2.4 mmol/g Resistance (non-woven) 120 .mu.m 88
.OMEGA. cm2 180 .mu.m 136 .OMEGA. cm2 Selectivity 97% Theoretical
IEC 1.92 meq/g
Different Dihalocarbons (Dihalo-Alkanes) Crosslinker
Investigation.
[0127] Different dihalo-ahalkanes e.g. dihalides crosslinkers such
as 1,6-diiodohexane, 1,5-dibromopentane, 1,6-dibromohexane and 1,10
dibromodecane were investigated. Casted membrane thickness was set
to 120 microns.
[0128] Membrane performance with these crosslinkers were
investigated.
TABLE-US-00004 Resistance Crosslinker [.OMEGA. cm.sup.2]
Selectivity [%] IEC [mmol/g] 1,6-Diiodohexane 1.48 97.1 2.22
1,6-Dibromohexane 1.96 97.5 2.48 1,10-Dibromodecane 2.15 97.6 2.42
1,5-Dibromopentane 2.82 97.3 2.67
[0129] For all samples selectivity was similar, but resistance
values differ. Different crosslinkers have different boiling points
and vapor pressure and also influence IEC of the membrane at
different levels. Moreover, longer molecules change polarity of
membranes and the distance between ion exchange groups.
1,6-diiodohexane and 1,6-dibromohexane show similar performance.
Membrane resistance is lower for 1,6-diiodohexane, but also IEC is
lower, which provides less interaction between counter ion and
fixed charges in the membrane matrix. 1,10-dibromodecane is very
comparable with 1,6-diiodohexane with respect to all performance.
1,5-dibromopentane has the highest resistance and highest IEC. This
effect is partly related with lower intermolecular distance and
higher ion exchange capacity.
[0130] Anion exchange membranes (AEM's) were cast from P(4-VPcS)
copolymer and were crosslinked with 1,6 diiodohexane. P(4-VPcS) AEM
membranes with a thickness of 40 micrometers were used to build a
capacitive deionization module with 18 cells, where a cell has two
electrodes, two current collectors, two membranes and a spacer. In
one stack P(4-VPcS) AEM membranes were used and in another stack
Neosepta CMX membranes. The cation exchange membrane was in both
cases Neosepta CMX. The feed water in these experiments was made
according to NSF 44 with a conductivity of 940 .mu.S/cm. All
experiments were done at room temperature with a flow of 1.2
l/min/m.sup.2 of spacer area. The operational cycle was 5 seconds
of pre-desalination, followed by 175 seconds of desalination and 90
seconds of electrode regeneration. The experiments were performed
with a set current of 5.5 A and 11 A during desalination and
regeneration respectively.
[0131] Vinyl Pyridine-Styrene Anion Exchange Membrane
Performance
TABLE-US-00005 Resistance Selectivity IEC Water uptake Sample No.
[.OMEGA. cm.sup.2] [%] [mmol/g] [%] 1 0.68 97.5 2.14 44 2 0.76 97.9
2.14 44 3 1.01 97.5 2.13 54 4 2.19 97.4 Average 1.16 97.6 2.14
47
[0132] The membranes have a good performance. Selectivity for all
samples is above 97%. Difference in resistance between samples
might be explained by variation in membrane thickness (from 38 to
84 .mu.m). Ion exchange capacity of 2.14 mmol/g corresponds to 82%
of group activation (2.14/2.62100%).
[0133] The voltage (V) profile versus time (s) was measured after 4
h of constant current operation (FIG. 4) and shows that voltage (V)
during water desalination (desal) for P(4-VPcS) membranes is
significantly lower than for the reference (Ref) membrane.
P(4-VPcS) membranes have lower resistance than the reference
membrane and will result in lower end voltage of the system.
Moreover, electrode regeneration (Reg) is more complete due to fact
that P(4-VPcS) membranes operate longer on constant current (later
reaching the voltage limit).
[0134] Membranes Performance after the Test
[0135] After 3 days, the test membrane permselectivity and
resistance was measured
TABLE-US-00006 Sample Resistance Selectivity IEC Wateruptake
Thickness No. [.OMEGA. cm.sup.2] [%] [mmol/g] [%] [.mu.m] 1.sup.st
0.77 96.7 2.16 23 71 5.sup.th 0.71 96.9 2.26 33 83 10.sup.th 0.99
96.7 2.29 39 68 14.sup.th 0.42 96.5 2.27 52 68
[0136] After the tests, P(4-VPcS) membrane resistance seems to be
on the same level as before the test. Membrane permselectivity and
ion exchange capacity remained also at the same level.
[0137] P(4-VPcS) anion exchange membranes have a high selectivity
for anions and at the same time a low resistance for ion transport.
Moreover, the vinyl pyridine-styrene film is mechanically strong
and therefore no additional reinforcement may be needed. These
membranes show potential for capacitive deionization systems, but
they may also be applied in various ion exchange processes.
[0138] In an embodiment, an anion exchange membrane with anion
exchange groups may be prepared by a method comprising: [0139]
reacting at least a first monomer comprising a benzene derivative
with a second monomer comprising a benzene derivative with a halide
group to form a copolymer; and [0140] reacting the pyridine
derivative of a crosslinker comprising at least a first pyridine
derivative group to the copolymer, with the copolymer to crosslink
the copolymer and at the same time to at least partially
functionalize the pyridine derivative to form an anion exchange
group.
[0141] The first and second monomer may comprise a vinyl group and
forming the copolymer may comprise providing an initiator and a
chain transfer agent to react the vinyl groups with each other to
polymerize the copolymer. The crosslinker may comprise two pyridine
derivative groups which may crosslink the copolymers and may be
functionalized to anion exchange groups.
[0142] There is further provided the use of a crosslinked copolymer
with ion exchange groups as described herein, an ion exchange
membrane as described herein, or an apparatus as described herein,
for the removal of ions from water.
[0143] These and other aspects, features and advantages will become
apparent to those of ordinary skill in the art from reading the
description and the appended claims. For the avoidance of doubt,
any feature of one aspect of the present invention may be utilized
in any other aspect of the invention. It is noted that the examples
given in the description below are intended to clarify the
invention and are not intended to limit the invention to those
examples per se. Similarly, all percentages are weight/weight
percentages unless otherwise indicated. Numerical ranges expressed
in the format "from x to y" or "x-y" are understood to include x
and y. When for a specific feature multiple preferred ranges are
described in the format "from x to y", it is understood that all
ranges combining the different endpoints are also contemplated.
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